Erythropoietic cells in the newt (Triturus cristatus) occur as homogeneous populations in the physiological response to induced anemia. Absolute rates of hemoglobin synthesis in different erythroid stages will be determined relative to cellular content of globin messenger RNA (mRNA) and ribosomal RNA. The onset of hemoglobin synthesis in the initial erythropoietic wave will be analyzed relative to the appearance of globin mRNA sequences. Since disproportionate synthesis of the four newt adult hemoglobins occurs in the initial wave, the qualitative and quantitative representation of the different hemoglobins represented in the globin mRNA fraction will be analyzed by mRNA translation in Xenopus laevis oocytes and by cDNA-mRNA hybridization. The molecular and cytological bases leading to restoration of the erythron will be sought, emphasizing the relationship between qualitative and quantitative aspects of hemoglobin synthesis, and globin mRNA. Analysis of non-globin proteins, including ferritin synthesis and the significance of ferritin in intracellular iron metabolism and hemoglobin synthesis, will be performed by means of incorporation studies utilizing labelled leucine and 59Fe and chase experiments in vitro where preferential labelling of ferritin can be achieved. The purpose of these studies is to define the extent to which transcriptional and translational phenomena are involved in RBC development and to evaluate the significnce of interactions between transcriptional and translational events in regulation of RBC development.